The prior art contains a number of references in various contexts which relate to the present invention.
U.S. Pat. No. 4,283,300, Kurtz, issued Aug. 11, 1981, discloses the hypochlorite-manganese staining problem in the context of toilet bowl treatment and teaches the use of an organic chelating agent, partially hydrolyzed polyacrylamide, to inhibit stain formation.
Commonly assigned U.S. patent application Ser. No. 234,535, Callicott, filed Feb. 17, 1981, teaches the use of an organic chelating agent, ethylene-maleic anhydride polymer, to inhibit stain formation caused by oxidation of Mn(II) to Mn(IV).
U.S. Pat. No. 4,115,293, Schoenholtz, issued Sept. 19, 1978, teaches the use of a variety of chelating agents, such as aminocarboxylates and polyphosphates (including metaphosphate) to inhibit the manganese staining of dentures when said denatures are soaked in an aqueous solution of potassium monopersulfate oxidizing agent.